This invention relates generally to a method and apparatus for increasing the emitted laser power of a speed and/or range detector, and more particularly, to a method and apparatus for increasing the laser power output of a LIDAR device for law enforcement speed measurement and for mapping and surveying by combining and reshaping the emitter source output in an optical fiber to increase the usable power while remaining compliant with laser safety regulations,
Laser speed and range measurement devices are widely utilized in traffic speed enforcement. The light detection and ranging (LIDAR) device emits a short pulse of infrared light that is directed in a narrow beam towards a selected target. The light pulse strikes the target and is typically reflected in all directions. A small portion of this light pulse is reflected back towards the LIDAR device. This return energy is collected and focused on a sensitive detector that then converts the light pulse energy to an electrical pulse. A high speed clock counts as the light pulse travels from the LIDAR device to the target and back to determine the total trip time. Using the known speed of light, an onboard computer determines the range to the target. For speed calculations, multiple ranges are taken and the change in range over a short period of time is determined.
Typically, police LIDAR speed guns and survey range finders such as disclosed in U.S. Pat. No. 5,221,956 to Patterson et al., use stripe array laser diode emitters to emit the pulse of infrared energy required to measure the distance to targets at significant ranges. The maximum range that a system can achieve is proportional to the amount of energy emitted per pulse by the laser.
The International Electrotechnical Commission (IEC) is a world-wide organization for standardization comprising all national electrotechnical committees. The object of the IEC is to invoke international cooperation on all questions concerning standardization in the electrical and electronic fields through publication of international standards. One such standard is IEC 825-1 which addresses safety of laser products. The IEC 825-1 standard determines limits through various properties of the laser, including wavelength, shape and size of source, pulse width, duration of pulse, and divergence. Most of these properties cannot be altered to allow more power output without detrimental effects in one or more of the other areas. The new IEC 825-1 standard (1993-11) changes the Accessible Emission Limits (AEL) for class 1 lasers.
The amount of energy that is emitted from these lasers is typically limited by the laser safety regulations of the country where the units are used. Most countries outside of the United States use the IEC 825 standard as a basis for their limits of laser output. The most recent version of this standard (1993-11) significantly limits the allowable laser output for what is termed xe2x80x9cclass onexe2x80x9d type laser systems especially when in the configurations used by laser speed guns and survey guns. These output limits impact the usefulness of the speed guns and survey products due to the resulting shorter range performance.
The IEC 825 standard determines limits through various properties of the laser, including wavelength, shape and size of source, pulse width, duration of pulse, and divergence, to name a few. Most properties cannot be altered to allow more power output without detrimental effects on other technical areas. The laser sources typically used in these types of devices are small stacks of stripe laser emitters. When these emitters are combined with the typical optics required for laser speed guns or survey devices, an angular source size is defined.
Generally, the IEC standard allows more power output for larger angular source sizes. The typical overall angular dimensions of these stripe array lasers are considered large according to the IEC standard. The IEC standard specifically addresses the allowable output power of laser arrays. According to the standard however, when evaluating an array, each emitter stripe must be evaluated separately. When evaluated separately, the size of each stripe is assumed to be equal to the smallest dimension. Because the stripes are very thin, any advantage gained by size of the emitter is eliminated because usable power is limited by the stripe configuration. Thus, the effectiveness of LIDAR speed guns and survey products is limited due to the resulting shorter range performance dictated by IEC 825.
It is therefore a primary object of the present invention to present a method and apparatus for increasing the power output of a laser emitter by increasing the apparent size of the emitter.
Another important object of the present invention is to provide a method and apparatus as aforesaid, which increases the apparent size of the smallest dimension of the emitter.
Yet another important object of the present invention is to provide a method and apparatus as aforesaid, which reshapes the laser emission.
Still another important object of the present invention is to provide a method and apparatus as aforesaid, which presents a generally circular apparent cross-section of the emitter.
Yet another important object of the present invention is to provide a method and apparatus as aforesaid, which increases the effective range of the LIDAR.
Another important object of the present invention is to provide a method and apparatus as aforesaid, which presents a homogeneous emitter output.
These and other objects of the present invention are achieved by injecting the output of a laser emitter into an optical fiber having a generally circular cross-section. The inside diameter of the optical fiber is greater than the smallest dimension of the laser emitter. Thus, the apparent size of the laser emitter at the output of the optical fiber allows an increase in the power output of the LIDAR, which is a function of the smallest dimension of the emitter.
Other objects and advantages of this invention will become apparent from the following description taken in connection with the accompanying drawings wherein is set forth by way of illustration and example, an embodiment of this invention.